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Doctoral defence in Biology - William Butler

Wed, 09/12/2020 - 14:00 to 16:00


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Ph.D. student: William Butler

Dissertation title: Modelling the dispersal and behaviour of fish early life-stages.

Dr. Alejandro Gallego, Oceanography Group Leader, Marine Scotland Science
Dr. Pierre Pepin, Research Scientist at DFO, Canada

Advisor: Dr. Guðrún Marteinsdóttir, Professor at the Faculty of Life and Environmental Sciences, University of Iceland

Doctoral committee: 
Dr. Steven Campana, Professor at the Faculty of Life and Environmental Sciences, University of Iceland
Dr. Øyvind Fiksen, Professor at the Faculty of Mathematics and Natural Sciences, University of Bergen, Norway

Chair of Ceremony: Dr. Anna Dóra Sæþórsdóttir, Professor and the Head of the Faculty of Life and Environmental Sciences, University of Iceland.

The population dynamics of marine fish are driven by many top-down and bottom-up processes operating across multiple life-history stages. The majority of teleosts produce large quantities of offspring which experience high mortality rates early in life. Changes in mortality during this period can therefore have large impacts on first year-class strength. As early-life stage mortality is generally driven by density-independent processes associated with the environment, a stock’s ability to produce large quantities of viable eggs influences the number of larvae that successfully settle. This causal relationship—from spawner to offspring—forms the backbone of this thesis. To examine the early-life stages, physical egg properties were measured, and a suite of models employed to understand the vertical positioning, dispersal patterns, and behavioural activities of fish eggs and larvae. The empirical results provided new species-specific information regarding the egg traits of two gadoids. The models highlighted the importance of including the following components into drift models: (1) intraspecific variation in egg density, (2) larval vertical migrations, and (3) a high temporal resolution. Furthermore, the location of spawning grounds is shown to greatly influence connectivity between spawning and nursery grounds. A simple method to capture adaptive vertical migrations in drift models is provided and a new approach to evaluating whether stocks are in a collapsed state is proposed. Taken together, the thesis provides novel data and insights into the early-life stages of commercially important Icelandic gadoids, and a series of recommendations and proposed methodologies for quantitatively evaluating aspects of marine population dynamics.

About the doctoral candidate:

William Butler completed his BSc in Marine Biology and Oceanography at the University of Southampton in 2006, and his MRes in Marine and Freshwater Ecology at the University of Glasgow in 2007. Prior to his doctoral studies at the University of Iceland, he worked as a water data analyst/modeller for the Scottish Environmental Protection Agency in Edinburgh. He currently works at the Marine and Freshwater Research Institute in Reykjavík, Iceland.

William Butler

Doctoral defence in Biology - William Butler